(Fortune Magazine) -- In 1990, things were coming together for John Barr. He'd left Morgan Stanley to launch Barr Devlin, an investment bank specializing in utility mergers. Around
the same time, he recalls, "a voice came into my head in the Caribbean dialect." He was driving back from a board meeting when it happened. "I've trained myself not to question when
that kind of thing happens," he says. "I pulled over. Wrote it down."

It sounded like this: "Things unseen count coup on you. The ant, wid its nose ... For necrosis try Ibn's toes, Ibn's ear, then turn away." Barr adds, "Over the next couple weeks
that voice kept speaking, and I compiled several thousand lines."

Much of it came on airplanes or at three in the morning, when Barr felt his mind was clearest. By the time his six-part epic poem (written in the voice of a black Caribbean poet
named Ibn Opcit) was published, he had already produced four volumes of poetry - and helped create the National Gas Clearinghouse, now Dynegy (Charts).

"To do two things at once is to do neither," Publius declared in his seventh maxim, circa 42 B.C. Barr clearly defied the maxim by doing both poetry and banking. Leonardo da Vinci
fit at least six careers into one lifetime. And there's a concert-level pianist named Condoleezza Rice who performs Brahms sonatas with Yo-Yo Ma when she's not busy with her side
gig at the State Department.

"Polymath" is the word we give people who master more than one field, and it's a rarefied bunch. Even Michael Jordan couldn't handle minor-league curve balls. So if you're unlikely
to become the world's top alligator wrestler and sales executive, should you pour your energies into one single-minded pursuit?

The short answer is no. The short explanation is plasticity.

Brain chemistry

Your brain, it turns out, isn't a fixed mass that shapes your behavior. Your behavior also shapes your brain. If a gardener takes up a serious interest in engineering, for instance,
her neurons form new pathways between previously isolated regions.

"It may well be a mistake to do just one thing," says Alvaro Pascual-Leone, a professor of neurology at Harvard Medical School. "If you practice multiple things you actually get
better at any one of those things." In other words the benefits of practicing one skill are not limited to that skill alone; they can be transferred.

Scientists are beginning to confirm this in research on how we learn motor skills. In a study published in 2004 in the Journal of Cognitive Neuroscience, Rachael Seidler at
the University of Michigan cast doubt on the traditional thinking that any motor skill we learn is limited to a particular context and task. She found instead that after having
subjects learn five different motor skills using joysticks, "subjects exposed to a variety of motor learning paradigms may be able to acquire general, transferable knowledge about
skill learning processes."

Science is showing evidence for what some have long felt are the benefits of cross-training your brain. Ask Gen. Peter Pace, chairman of the Joint Chiefs of Staff, why his
undergraduate training in nuclear propulsion systems remains indispensable. "I'm not applying those exact skills every day, but it taught me ways to think through problems -
visualizing, conceptualizing - that I do use every day," he told Fortune last year. "Your mind touches on these resources and you're not even conscious of it."

To strengthen those neural pathways, however, we have to repeatedly do something. "It's sort of like walking on the beach," says Pascual-Leone. "Every time you do it, you change the
sand. But unless you keep stepping on the same piece of sand, you won't leave a permanent mark." Leafing through a how-to book on nuclear propulsion systems won't do it.

Varying skills

The more varied our skills, moreover, the more varied the neural pathways in use. "They're kind of reservoirs in your consciousness that you can reach back into for insights you're
applying to something totally dissimilar," says Pete Dawkins, vice chairman of Citigroup's global-wealth management. "I think the broader, the more of these reservoirs you have
available, the more likely you can see through the fog."

Dawkins's own résumé is hard to top. He has been, at varying points of his life, a brigadier general in the Army, a partner at Lehman Brothers, head of consulting at Bain,
a Rhodes Scholar, and a student at Princeton's Woodrow Wilson School, where he earned his Ph.D. Also: a Heisman Trophy winner (in 1958).

Dawkins's conversations with Fortune looped from the super-ellipse (a mathematical figure that's used in urban planning) to British linguistic philosophy, which he studied in
his 20s at Oxford. "It's the whole exhaustive study of what words and phrases mean," he says. "I didn't think of the significance of this then, but I now find it fascinating how
often people are arguing when they don't disagree at all. They're just being imprecise about how they're defining things. It has trained my mind. Like a video stream, I think in two
levels: What is the person saying, and what do they really mean?"

John Barr, the poet, also has experienced a life on two levels. "The venue of business is the world of external affairs," he notes. "The venue of a poet is the world of interior
reality."

Over time Barr came to see hidden commonalities in his twin pursuits. "They're both in the business of making order out of chaos," he says. Grappling with a very different set of
conundrums produced a sensibility that eventually bled into his day job. "The prolonged exposure to poetry has made me more willing to tolerate ambiguity," he says. "I think that's
made me a better advisor to my clients and a better decision-maker."

So the next time you're considering how to recommit to your job and get better at it, broaden your idea of what it takes to be excellent. Embrace the irrelevant. "I feel very
fortunate," says Dawkins of his varied interests. "I think it's given a lot more texture to my life than if I'd followed a single path."

And more often than you'd expect, those different paths converge. When the Poetry Foundation received a stunning gift of $180 million in late 2002, it went looking for a new
president to map out its financial future. It found John Barr.